• Title/Summary/Keyword: Eddy covariance

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On Using the Eddy Covariance Method to Study the Interaction between Agro-Forest Ecosystems and the Atmosphere (농림생태계와 대기간의 상호 작용 연구를 위한 에디 공분산 방법의 사용에 관하여)

  • Choi Taejin;Kim Joon;Yun Jin-il
    • Korean Journal of Agricultural and Forest Meteorology
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    • v.1 no.1
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    • pp.60-71
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    • 1999
  • The micrometeorological tower flux network is the cornerstone of the global terrestrial vegetation monitoring. The eddy covariance technique used for tower fluxes is derived from the conservation of mass and is most applicable for steady-state conditions over flat, extended, and uniform vegetation. This technique allows us to obtain surface fluxes of energy budget components, greenhouse and trace gases, and other pollutants. The quality-controlled flux data are invaluable to validate various models with temporal scales ranging from minutes to years and spatial scales ranging from a few meters to hundreds of kilometers. In this paper, we review the theoretical background of this important eddy covariance technique, examine the measurement criteria and corrections, and finally suggest some measurement strategies that may facilitate coordinated flux measurements among different disciplines and provide a strong infrastructure for the global flux network.

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Comparison of Soil Evaporation Using Equilibrium Evaporation, Eddy-Covariance and Surface Soil Moisture on the Forest Hillslope (산림 사면에서 토양수분 실측 자료, 평형증발 및 에디-공분산방법을 이용한 토양증발비교)

  • Gwak, Yong-Seok;Kim, Sang-Hyun;Kim, Su-Jin
    • Journal of Environmental Science International
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    • v.22 no.1
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    • pp.119-129
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    • 2013
  • We compared equilibrium evaporation($E_{equili}$) eddy-covariance($E_{eddy}$) with soil moisture data($E_{SMseries}$) which were measured with a 2 hours sampling interval at three points for a humid forest hillslope from May 5th to May 31th in 2009. Accumulations of $E_{eddy}$, $E_{equili}$ for the study period were estimated as 2.52, 3.28 mm and those of $E_{SMseries}$ were ranged from 1.91 to 2.88 mm. It suggested that the eddy-covariance method considering the spatial heterogeneity of soil evaporation is useful to evaluate the soil evaporation. Method A, B and C were proposed using mean meterological data and daily moisture variation and the computations were compared to eddy-covariance method and equilibrium evaporation. The methods using soil moisture data can describe the variations of soil evaporation from eddy-covariance through simple moving average analysis. Method B showed a good matched with eddy-covariance method. This indicated that Dry Surface Layer (DSL) at 14:00 which was used for method B is important variable for the evaluation of soil evaporation. The total equilibrium evaporation was not significantly different to those of the others. However, equilibrium evaporation showed a problem in estimating soil evaporation because the temporal tendency of $E_{equili}$ was not related with the those of the other methods. The improved understanding of the soil evaporation presented in this study will contribute to the understandings of water cycles in a forest hillslope.

Surface Flux Measurements at King Sejong Station in West Antarctica: I. Turbulent Characteristics and Sensible Beat Flux (남극 세종기지에서의 지표 플럭스 관측: I. 난류 특성과 현열 플럭스)

  • Choi, Tae-Jin;Lee, Bang-Yong;Lee, Hee-Choon;Shim, Jae-Seol
    • Ocean and Polar Research
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    • v.26 no.3
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    • pp.453-463
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    • 2004
  • The Antarctic Peninsula is important in terms of global warming research due to pronounced increase of air temperature over the last century. The first eddy covariance system was established at King Sejong Station located in the northern region of the Antarctic Peninsula in December of 2002 and has been operated over one year. Here, we analyze turbulent characteristics to determine quality control criteria for turbulent sensible heat flux data as well as to diagnose the possibility of long term eddy covariance measurement under extreme weather conditions of the Antarctic Peninsula. We also report the preliminary result on sensible heat flux. Based on the analyses on turbulent characteristics such as integral turbulence characteristics of vertical velocity (w) and heat (T), stationarity test and investigation of correlation coefficient, they fallow the Monin-Obukhov similarity and eddy covariance flux data were reliable. ${\sim}47%$ of total retrieved sensible heat flux data could be used for further analysis. Daytime averaged sensible heat flux showed a pronounced seasonal variation, with a maximum of up to $300Wm^{-2}$ in summer. In conclusion, continuous and long-term eddy covariance measurement may be possible at the study site and the land surface may influence the atmosphere significantly through heat transport in summer.

Can $CO_2$ concentration at one level of eddy covariance measurement be used to estimate storage term over forest\ulcorner

  • Choi, Tae-Jin;Chae, Nam-Yi;Kim, Joon;Lim, Jong-Hwan
    • Proceedings of the Korean Environmental Sciences Society Conference
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    • 2003.11a
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    • pp.47-50
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    • 2003
  • $CO_2$ concentration profile was measured to investigate whether $CO_2$ concentration at one level (i.e., eddy covariance measurement level) can be used to estimate storage term without significant uncertainty at broadleaf deciduous forest at Kwangneung experiment forest in Korea. Based on t-test with significance level of 5%, there was no statistical difference between storage term from one-level $CO_2$ concentration and one from $CO_2$ profile measurement. Storage term constitutes on average 5% of half hourly net ecosystem exchange (NEE) even at unstable stability (i.e., well mixed condition), indicating that storage term should be considered even at daytime, which is sometimes neglected.

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Estimation of Satellite-based Spatial Evapotranspiration and Validation of Fluxtower Measurements by Eddy Covariance Method (인공위성 데이터 기반의 공간 증발산 산정 및 에디 공분산 기법에 의한 플럭스 타워 자료 검증)

  • Sur, Chan-Yang;Han, Seung-Jae;Lee, Jung-Hoon;Choi, Min-Ha
    • Korean Journal of Remote Sensing
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    • v.28 no.4
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    • pp.435-448
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    • 2012
  • Evapotranspiration (ET) including evaporation from a land surface and transpiration from photosynthesis of vegetation is a sensitive hydrological factor with outer circumstances. Though both direct measurements with an evaporation pan and a lysimeter, and empirical methods using eddy covariance technique and the Bowen ratio have been widely used to observe ET accurately, they have a limitation that the observation can stand for the exact site, not for an area. In this study, remote sensing technique is adopted to compensate the limitation of ground observation using the Moderate Resolution Imaging Spectroradiometer (MODIS) multispectral sensor mounted on Terra satellite. We improved to evapotranspiration model based on remote sensing (Mu et al., 2007) and estimated Penman-Monteith evapotranspiration considering regional characteristics of Korea that was using only MODIS product. We validated evapotranspiration of Sulma (SMK)/Cheongmi (CFK) flux tower observation and calculation. The results showed high correlation coefficient as 0.69 and 0.74.

Errors in Net Ecosystem Exchanges of CO2, Water Vapor, and Heat Caused by Storage Fluxes Calculated by Single-level Scalar Measurements Over a Rice Paddy (단일 높이에서 관측된 저장 플럭스를 사용할 때 발생하는 논의 이산화탄소, 수증기, 현열의 순생태계교환량 오차)

  • Moon, Minkyu;Kang, Minseok;Thakuri, Bindu Malla;Lee, Jung-Hoon
    • Korean Journal of Agricultural and Forest Meteorology
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    • v.17 no.3
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    • pp.227-235
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    • 2015
  • Using eddy covariance method, net ecosystem exchange (NEE) of $CO_2$ ($F_{CO_2}$), $H_2O$ (LE), and sensible heat (H) can be approximated as the sum of eddy flux ($F_c$) and storage flux term ($F_s$). Depending on strength and distribution of sink/source of scalars and magnitude of vertical turbulence mixing, the rates of changes in scalars are different with height. In order to calculate $F_s$ accurately, the differences should be considered using scalar profile measurement. However, most of flux sites for agricultural lands in Asia do not operate profile system and estimate $F_s$ using single-level scalars from eddy covariance system under the assumption that the rates of changes in scalars are constant regardless of the height. In this study, we measured $F_c$ and $F_s$ of $CO_2$, $H_2O$, and air temperature ($T_a$) using eddy covariance and profile system (i.e., the multi-level measurement system in scalars from eddy covariance measurement height to the land surface) at the Chengmicheon farmland site in Korea (CFK) in order to quantify the differences between $F_s$ calculated by single-level measurements ($F_s_{-single}$ i.e., $F_s$ from scalars measured by profile system only at eddy covariance system measurement height) and $F_s$ calculated by profile measurements and verify the errors of NEE caused by $F_s_{-single}$. The rate of change in $CO_2$, $H_2O$, and Ta were varied with height depending on the magnitudes and distribution of sink and source and the stability in the atmospheric boundary layer. Thus, $F_s_{-single}$ underestimated or overestimated $F_s$ (especially 21% underestimation in $F_s$ of $CO_2$ around sunrise and sunset (0430-0800 h and 1630-2000 h)). For $F_{CO_2}$, the errors in $F_s_{-single}$ generated 3% and 2% underestimation of $F_{CO_2}$ during nighttime (2030-0400 h) and around sunrise and sunset, respectively. In the process of nighttime correction and partitioning of $F_{CO_2}$, these differences would cause an underestimation in carbon balance at the rice paddy. In contrast, there were little differences at the errors in LE and H caused by the error in $F_s_{-single}$, irrespective of time.

A Preliminary Flux Study for CO2 and Biogenic VOCs in a Forest (산림지역 이산화탄소 및 자연적휘발성유기화합물의 교환량 관측기법 기초연구)

  • Kim, So-Young;Kim, Su-Yeon;Choi, Soon-Ho;Kim, Sae-Wung
    • Journal of Korean Society for Atmospheric Environment
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    • v.28 no.5
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    • pp.485-494
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    • 2012
  • The purpose of this study is to monitor the flux of $CO_2$ and BVOCs (biogenic volatile organic compounds) between the atmosphere and forest. The main research activities are conducted at Taehwa Research Forest (TRF), managed by the College of Agriculture and Life Sciences at Seoul National University. The TRF site is located 60 km north-east from the center of Seoul Metropolitan Area. The TRF flux tower is in the middle of a Korean Pine (Pinus Koraiensis) plantation ($400m{\times}400m$), surrounded by a mixed forest. Eddy covariance method was used for $CO_2$ flux above the forest and REA (Relaxed eddy accumulation) method applying eddy covariance was used for BVOCs flux. BVOCs flux that was measured in spring (from May 16 to 18) had distribution of 84 to $2917{\mu}g/m^2{\cdot}h$. Especially, it showed that d-limonene being strong reactivity composed the largest fraction of monoterpene. Ambient $CO_2$ concentration measured in Mt. Taehwa was 399 ppm and observed $CO_2$ fluxes between the atmosphere and forest suggested that during the day, $CO_2$ is absorbed by plants through photosynthesis and released during the night.

Quality Control and Assurance of Eddy Covariance Data at the Two KoFlux Sites (KoFlux 관측지에서 에디 공분산 자료의 품질관리 및 보증)

  • Kwon, Hyo-Jung;Park, Sung-Bin;Kang, Min-Seok;Yoo, Jae-Il;Yuan, Renmin;Kim, Joon
    • Korean Journal of Agricultural and Forest Meteorology
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    • v.9 no.4
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    • pp.260-267
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    • 2007
  • This research note introduces the procedure of the quality control and quality assurance applied to the eddy covariance data collected at the two KoFlux sites (i.e., Gwangneung forest and Haenam farmland). The quality control was conducted through several steps based on micrometeorological theories and statistical tests. The data quality was determined at each step of the quality control procedure and was denoted by five different quality flags. The programs, which were used to perform the quality control, and the quality assessed data are available at KoFlux website (http://www.koflux.org/).

Estimation and Comparison of Carbon Uptake in Rice Paddy, Dry Cropland and Grove in South Korea using Eddy Covariance Flux Data (에디 공분산 플럭스 자료를 이용한 논, 밭, 과수원의 연간 탄소 흡수량 추정 및 비교)

  • Hur, Jina;Shim, Kyo-Moon;Lee, ByeongTae;Kim, Yongseok;Jo, Sera
    • Korean Journal of Environmental Agriculture
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    • v.39 no.4
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    • pp.334-342
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    • 2020
  • BACKGROUND: To quantify carbon exchange at agricultural ecosystems in South Korea, net ecosystem exchange (NEE) at three croplands including a rice paddy, a bean field and an apple orchard was measured on the basis of the eddy covariance technique. METHODS AND RESULTS: NEE of CO2 during the growing season (June to September) averaged over the recent two years (2018-2019) was the highest at rice (-4.49 g C m-2 day-1), followed by the bean (-3.12 g C m-2 day-1) and apple (-0.93 g C m-2 day-1). The diurnal variation of NEE was the highest at the rice, while the seasonal variation of it was the highest at the bean than others. In terms of yearly variation, the rice paddy and the bean field absorbed more CO2 in 2019 compared to 2018, while the apple orchard absorbed less. CONCLUSION: Our results confirmed that these croplands consistently acted as net sinks for CO2 during the growing season because an amount of CO2 uptake from photosynthesis was larger than one of its emissions from respiration. The quantification of net CO2 exchange at agricultural ecosystems may help to better understand the local carbon cycle over various time scales.

Real Time Monitoring and Simulation System (RTMASS) for Tak Flux Measurement Site, Thailand (태국 Tak 플럭스 관측소의 실시간 자료 감시 및 모사 시스템)

  • Wonsik Kim;Hyungjun Kim;Joon Kim;Yasushi Agata;Shin Miyazaki;Taikan Oki
    • Korean Journal of Agricultural and Forest Meteorology
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    • v.5 no.2
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    • pp.116-127
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    • 2003
  • The Tak flux measurement (TFM) site, one of the sites of Korean Flux Network (KoFlux) which is an infrastructure of AsiaFlux, is constructed at a northwest of Thailand. The eddy covariance technique is used for measuring energy, water and carbon dioxide ($CO_2$) fluxes, and a real time monitoring and simulation system (RTMASS) developed for data acquisition and processing. The RTMASS is the core structure of the KoFlux-data information system (KoFlux-DIS) and consisted of a remote and a local system. Data acquisition and transmission, and data storage, processing and publishing are functions of those systems, respectively. As primary results about the characteristics of mean flow and turbulence analysis, TFM is a proper site to measure and analyze the various fluxes and those budgets on tropical deciduous forest.